1. Field of the Invention
The present invention relates to a control apparatus for a synchronous generator system for converting kinetic energy to electric power, and more particularly to a control apparatus which does not require the provision any sensor, such as an encoder, hole elements and so on, for detecting the position of rotating magnetic poles of a synchronous generator. Further, the present invention relates to a hybrid-type electric vehicle, to which the synchronous generator control apparatus as mentioned above is applied.
2. Description of Related Art
There is known a hybrid-type electric vehicle, in which an internal combustion engine as well as an electric motor and/or generator are used in combination as a driving power source, for the purpose of improving the fuel consumption and the exhaust gas purification. In such an electric vehicle, it is desired that an electric vehicle under a standstill state can only be started electrically.
By the way, as a motor or a generator for use in an electric vehicle of this kind, a synchronous type machine is usually utilized. As is well known, the positional relationship between a stator and a rotor thereof must necessarily to be found, in order to operate the synchronous machine.
In a conventional control apparatus of this kind, there has been provided a position sensor for detecting the position of rotating magnetic poles of a synchronous machine. However, such a position sensor is very expensive, with the result that the whole cost of the control apparatus increases. Further, such a sensor also increases the size of the control apparatus as a whole.
To solve the problems as described above, the Japanese Patent Application laid-open No. 9-163507 (published Jun. 20, 1997) proposes a so called sensorless synchronous machine system, in which a control computer carries out a predetermined processing to presume the position of magnetic poles of a synchronous machine.
It is well known that the voltage induced across a winding of a certain phase has a phase difference of 90.degree. from the magnetic flux produced by a magnetic pole. The prior art as disclosed in the JP-A-9-163507 utilizes the aforesaid known fact, and the control computer takes therein a signal concerning the induced voltage and executes a predetermined processing to presume the position of the magnetic poles.
However, the prior art as described above operates on the assumption that the phase difference between the phase voltage and the magnetic flux is equal to 90.degree.. This assumption is quite correct under the condition wherein a synchronous machine is not loaded. However, the phase difference does not become equal to from 90.degree., as a load current flows through the synchronous machine. Namely, the position of the magnetic poles can not be presumed exactly under the loaded condition of the synchronous machine.